Belongs within: Orthoceratia.Contains: Spyroceras. The Pseudorthoceratidae were a Lower Silurian to Permian family of ‘orthocerid’ cephalopods. The relationship of this family to the remaining orthocerids is doubtful. Characters (from Sweet 1964): Cyrtochoanitic orthocones and longiconic cyrtocones; endosiphuncular annuli developing into continuous parietal endosiphuncular lining, each deposit extending forward or backward from its place of origin… Continue reading Pseudorthoceratidae


Belongs within: Orthoceratia.Contains: Cycloceras, Dawsonoceratidae, Orthoceratidae, Paraphragmitidae, Geisonoceratidae. The Michelinoceratida or Orthocerida were a Lower Ordovician to Upper Triassic assemblage of orthoconic or cyrtoconic cephalopods. This is perhaps the most systematically difficult group of fossil cephalopods and may be polyphyletic, with recent authors suggesting that some families (particularly the Pseudorthoceratidae) should be removed from the… Continue reading Orthoceratida


Belongs within: Orthoceratia. The Lower to Middle Ordovician Baltoceratidae were a family of relatively large orthoconic early cephalopods. Characters (from Furnish & Glenister 1964): Smooth, longiconic orthocones with moderately large marginal siphuncle, orthochoanitic septal necks and thin homogenous connecting rings. Baltoceratidae [Cochlioceratidae]K93 |–Murrayoceras Foerste 1926FG64 | `–*M. murrayi (Billings 1857) [=Orthoceras murrayi]FG64 |–Ogygoceras Ulrich, Foerste… Continue reading Baltoceratidae


Belongs within: Orthoceratia. The Proteoceratidae were a Middle Ordovician to Middle Silurian family of orthocerid cephalopods. Characters (from Sweet 1964): Smooth or annulated orthocones and exogastric cyrtoconeswith expanded cyrtochoanitic siphuncular segments in early stages and narrower, subcylindrical, orthochoanitic segments in later stages. Siphuncular deposits consist of annuli developing into parietal deposits by growth forward, backward,… Continue reading Proteoceratidae


Belongs within: Pseudorthoceratidae. Spyroceras is a Devonian genus of orthocerid cephalopod recorded from Europe and North America. Characters (from Sweet 1964): Annulated orthocones with straight transverse sutures, transverse or slightly oblique surface annulations, and faintly cyrtoconic apices. Surface variously ornamented, longitudinal lirae conspicuous from earliest stage. Siphuncle central or slightly ventral; siphuncle orthochoanitic with forward-growing… Continue reading Spyroceras


Belongs within: Orthoceratia. The Troedssonellidae were a Lower to Middle Ordovician family of orthocerid cephalopods that formed endocones in the apical part of their siphuncles. Characters (from Sweet 1964): Siphuncle suborthochoanitic; continual endosiphuncular lining of parietal deposits prolonged adapically to form endocones. Troedssonellidae [Buttsoceratidae, Troedssonellina]S64 |–Tajaroceras wardae Hook & Flower 1976K93 |–Moridunoceras Evans 2005KE19 |–Oxfordoceras… Continue reading Troedssonellidae


Belongs within: Orthoceratidae. Orthoceras is a Middle Ordovician genus of large orthocerid cephalopods. Characters (from Sweet 1964): Slightly expanding, almost cylindrical orthocones or faintly exogastric cyrtocones; siphuncle empty, cylindrical, suborthochoanitic, subcentral to slightly ventral. Body chamber transversely constricted at mid-length and marked by single longitudinal dorsal and two longitudinal ventral depressions. Surface ornamented by network… Continue reading Orthoceras


Belongs within: Orthoceratida.Contains: Orthoceras. The Orthoceratidae includes orthocerid cephalopods from the Lower Ordovician to Upper Triassic; however, it is mostly defined by negative characteristics and its monophyly is potentially suspect. Some orthoceratids reached very large sizes. Characters (from Sweet 1964): Smooth or elaborately ornamented conchs, generally subcircular in cross-section; central or subcentral siphuncle generally lacking… Continue reading Orthoceratidae


Belongs within: Orthoceratida. The Geisonoceratidae were a Middle Ordovician to Middle Devonian family of orthocerid cephalopods distinguished by their siphucular structure. Characters (from Sweet 1964): Orthoconic or cyrtoconic conchs with subcircular cross-section; orthochoanitic to suborthochoanitic siphuncle occupied by endosiphuncular annuli restricted to septal foramen or growing anteriorly against connecting rings; endosiphuncular annuli in advanced species… Continue reading Geisonoceratidae


Belongs within: Orthoceratida. The Middle Silurian Paraphragmitidae were orthoconic or cyrtoconic orthocerid cephalopods with a distinctly annulated shell. Characters (from Sweet 1964): Annulated orthocones, cyrtocones and brevicones; siphuncle empty, subcentral, suborthochoanitic. <==Paraphragmitidae |–Arterioceras concavum Zhuravleva 1978K93 |–Paraphragmites Flower 1943S64 | `–*P. ascoceroides Flower 1943S64 |–Calocyrtoceras Foerste 1936S64 | `–*C. cognatum (Barrande 1866) [=Cyrtoceras cognatum]S64 |–Cyrtocycloceras… Continue reading Paraphragmitidae